Deck 12: Field-Effect Transistors

Question 1

The terminal is the JFET counterpart of the BJT base terminal.

A) gate
B) drain
C) source

Answer 1

gate

Question 2

JFETs are

A) current-controlled devices.
B) voltage-controlled devices.
C) frequency-controlled devices.
D) impedance-controlled devices.

Answer 2

voltage-controlled devices.

Question 3

A JFET has the following ratings: VGSoff) = -2 V to -5 V and IDSS = 4 mA to 12 mA. The device is being used in a voltage divider circuit. When the load line is plotted, it is found that the VGS for the circuit has a range of -1 V to -3.5 V. What are the corresponding Qmax) values?

A) VGSQ = -1 V, IDQ = 7.68 mA
B) VGSQ = -3.5 V, IDQ = 1.1 mA
C) VGSQ = -1 V, IDQ = 1 mA
D) Cannot be determined with the information given.

Answer 3

VGSQ = -3.5 V, IDQ = 1.1 mA

Question 4

A JFET has values of IDSS = 12 mA and VGSoff) = -4 V. What is the value of ID at VGS = -8 V?

A) 12 mA
B) 0 mA
C) 4 mA
D) 2 mA

Question 5

The value of gm is always the value of gm0 for a given JFET.

A) less than
B) equal to
C) less than or equal to
D) greater than

Question 6

The region of the JFET drain curve that lies between pinchoff and breakdown is called

A) the constant-voltage region.
B) the ohmic region.
C) the constant-current region.
D) Both B and C above.

Question 7

A JFET has the following ratings: VGSoff) = -2 V to -5 V and IDSS = 4 mA to 12 mA. This device is being used in a self-bias circuit. When the bias line for the device is plotted, it is found that VGS for the circuit will have a range of -1 V to -2.5 V. What are the corresponding Qmin) values?

A) VGSQ = -1 V, IDQ = 1 mA
B) VGSQ = -2.5 V, IDQ = 250 μA
C) VGSQ = -1 V, IDQ = 7.86 mA
D) Cannot be determined with the information given.

Question 8

The value of ID is always the value of IDSS for a given JFET.

A) less than
B) equal to
C) less than or equal to
D) greater than

Question 9

Which of the following is usually used to control the channel width of a given JFET?

A) VS
B) VGS
C) The operating frequency
D) ID

Question 10

As the channel width of a JFET decreases, the source-to-drain resistance of the device

A) increases.
B) decreases.

Question 11

A JFET has values of IDSS = 10 mA and VGSoff) = -5 V. What is the value of ID at VGS = -3 V?

A) 1.6 mA
B) 3.6 mA
C) 25.6 mA
D) 4 mA

Question 12

A JFET has the following ratings: VGSoff) = -2 V to -5 V and IDSS = 4 mA to 12 mA. The device is being used in a gate bias circuit with a gate supply voltage of VGG = -1 V. What is the difference between the minimum and maximum values of ID for the circuit?

A) 7.68 mA
B) 9.6 mA
C) 6.68 mA
D) 8.6 mA

Question 13

The value of VDS that causes ID to reach its maximum value at a constant value of VGS is called

A) VDmax).
B) pinchoff voltage.
C) VDSS.
D) None of these is correct.

Question 14

A given JFET has values of Vp = +10 V and IDSS = 8 mA. What is the value of VGSoff) for the device?

A) +10 V
B) -10 V
C) -5 V
D) Cannot be determined from the information given.

Question 15

Which of the JFET biasing circuits listed below provides the best Q-point stability?

A) Gate-bias
B) Self-bias
C) Voltage-divider bias
D) Current-source bias

Question 16

Which of the following statements is true?

A) JFET drain current is controlled by its input gate) current.
B) JFET channel width is controlled by its gate-source voltage.
C) There is only one way to vary JFET channel width.
D) JFET drain current at a given drain supply voltage) varies inversely with channel width.

Question 17

The terminal is the JFET counterpart of the BJT emitter terminal.

A) gate
B) drain
C) source

Question 18

A given JFET has values of gm0 = 1200 μS and VGSoff) = -4 V. What is the value of gm for the device at VGS = -2 V?

A) 600 μS
B) 1200 μS
C) 300 μS
D) Cannot be determined with the information given.

Question 19

The terminal is the JFET counterpart of the BJT collector terminal.

A) gate
B) drain
C) source

Question 20

The JFET uses a positive drain supply voltage VDD).

A) n-channel
B) p-channel

Question 21

The amplifier has low input impedance, high output impedance, and high voltage gain.

A) common-gate
B) common-drain
C) common-source

Question 22

The amplifier has high input impedance, low output impedance, and low-voltage gain.

A) common-gate
B) common-drain
C) common-source

Question 23

A given JFET has values of gm0 = 1200 μs and VGSoff) = -4 V. What is the approximate value of IDSS?

A) 4.8 mA
B) 9.6 mA
C) 2.4 mA
D) Cannot be determined with the information given.

Question 24

A given JFET has values of gm0 = 1000 μS and VGSoff) = -6 V. The device is being used in a common-source amplifier with values of RD = 2.2 kΩ, RL = 10 kΩ, and VGS = -1V. What is the value of Av for the circuit?

A) 1.5
B) 2.2
C) 10
D) Cannot be determined with the information given.

Question 25

In a JFET amplifier, VGS = -5 V, IG = 0 mA, and ID = IS = 5mA. Which of the following statements is true?

A) The gate terminal of the JFET is probably open.
B) The gate-source junction of the JFET is probably shorted.
C) The drain terminal of the JFET is probably open.
D) The readings do not indicate that any problem exists.

Question 26

The JFET in Figure has the following ratings: VGSoff) = -5 V and gm0 = 4000 μS. What is the value of Av for the circuit?

A) 1.2
B) 1.47
C) 0.4
D) 0.9

Question 27

The JFET in Figure has the following ratings: VGSoff) = -2 V to -10 V, gm0 = 1000 μS to 1600 μS. What is the approximate input impedance of the circuit?

A) 179 kΩ
B) 1 MΩ
C) 848 kΩ
D) 922 kΩ

Question 28

Assume that the JFET has values of IDSS = 12 mA and VGSoff) = -6 V. If VGG = -3 V, what is the value of ID for the circuit?

A) 1 mA
B) 3 mA
C) 4.55 mA
D) 6 mA

Question 29

In a JFET amplifier, VGS = -2 V and ID = IDSS. Which of the following statements is true?

A) The gate terminal of the JFET is probably open.
B) The gate-source junction of the JFET is probably shorted.
C) The drain terminal of the JFET is probably open.
D) The readings do not indicate that any problem exists.

Question 30

Gate-source breakdown voltage can be defined as

A) the value gate-source voltage that will allow the channel to break down and conduct.
B) the value of gate-source voltage that will damage the JFET.
C) the maximum allowable value of VGS.
D) None of the above.
Chapter 12 Field-Effect Transistors Answer Key

Question 31

The high input impedance of a JFET amplifier prevents it from being used as a buffer.

Question 32

One advantage of using a JFET rf amplifier over a BJT amplifier is

A) high input impedance.
B) The JFET requires no signal input current.
C) The JFET is less susceptible to noise.
D) All of the above.